1. Industrial Field
The present invention relates to a method of manufacturing a multilayered printed wiring board by a buildup system in which a conductive circuit layer and an insulating layer are alternately piled up, said method further comprising using an adhesive film to easily manufacture such multilayered printed wiring board excellent in surface smoothness in satisfactory yields.
2. Prior Art
In recent years, techniques of manufacturing a multilayered printed wiring board by a buildup method of alternately piling up an organic insulating layer on a conductor layer of an inner-layer circuit board are drawing attention. Above all, with the progress of a laser processing technique, a method of manufacturing a multilayered printed wiring board which method comprises covering an inner-layer circuit substrate with a copper foil provided with a thermosetting resin or directly with a thermosetting resin, followed by performing curing by heating, performing perforating with a laser and/or a drill, and forming the conductor layer by plating, has been broadly used. In Japanese Patent Application Laid-Open (Kokai) No. 87927/1999, the present inventors have also disclosed an adhesive film which uses a thermal fluid resin composition capable of filling a circuit through hole and which is excellent in the properties for covering an inner-layer circuit pattern, and a method of manufacturing a similar multilayered printed wiring board using the adhesive film. Japanese Patent Application Laid-Open (Kokai) No. 87927/1999 discloses a method of vacuum-laminating the thermosetting resin composition layer supported by a support base film on a circuit substrate substantially at 80xc2x0 C.xc3x975 seconds before thermally curing the thermosetting resin, but fails to refer to the subsequent step of thermally curing the resin composition.
If a resin composition layer is vacuum-laminated on a circuit substrate with the support base film not having been stripped, followed by stripping the support base film, and curing the resin composition, foreign matters stick during thermally curing of the resin, which may cause later on the problems of disconnection, short-circuit, and other defects. Moreover, concerning a built-up substrate made by these processes, as can be seen from FIG. 1, since a circuit or a via cannot be formed on the via and/or the through hole, the degree of freedom is limited in design, it is difficult to use an automatic arrangement wiring tool, and much time is disadvantageously required in circuit design.
As a method of solving such defects, techniques of filling the via and/or the through hole with a hole filling ink or a conductive paste are known. A surface smoothing process of a conventional built-up substrate will be described with reference to FIG. 2. First, a thermosetting resin is applied or laminated on an inner-layer circuit substrate pattern, followed by thermally curing. Subsequently, perforating is performed with a laser and/or a drill. Subsequently, the resin surface is subjected to a roughing treatment with an alkaline oxidizer or the like, and then a conductor layer is formed by plating. Even when a copper foil provided with a thermosetting resin is used, conductor connection is performed in the hole by plating to form a similar structure. Thereafter, the hole is filled with a hole filling ink or a conductive paste by screen printing, and the thermal curing is performed. Subsequently, by polishing the surface and forming the conductor layer once again by plating, it becomes possible to form a circuit on the via or the through hole.
According to the conventional method, as has been described above, it is necessary to manufacture a hole filling screen print with good precision for each pattern of the via and/or the through hole, additionally a step of polishing the surface to remove the hole filling ink or the conductive paste having stuck out in the vicinity of the printed surface is essential, and therefore, there is the problem that the overall process gets lengthened and complicated.
It is an object of the present invention to develop a method of preventing foreign matters particularly from being mixed in a thermally cured resin composition surface, and thereby manufacturing easily a multilayered printed wiring board superior in surface smoothness, upon curing thermally a resin composition layer of an adhesive film provided with a support base film on a circuit substrate in good yields.
The present inventors have found that the problem can be solved by preventing the thermosetting resin composition from directly contacting the air outside until it is thermally cured, and have solved the defect that foreign matters stick to the resin during being cured.
Accordingly, according to the present invention, there is provided as a first embodiment thereof a method of manufacturing a multilayered printed wiring board using an adhesive film comprising a support base film provided with a mold release layer and a thermosetting resin composition laminated on the surface of the mold release layer, said resin composition being provided with the same or smaller area as or than that of the support base film, provided with thermal fluidity, and being solid at normal temperatures,
said method further comprising essentially the steps of:
1) directly covering at least the pattern processed portion on one surface or both surfaces of a pattern processed circuit substrate with the resin composition layer of said adhesive film, and performing laminating by heating and pressurizing under a vacuum condition;
2) thermally curing the resin composition with the support base film being attached thereto;
3) uncovering the resin composition layer by stripping at least the support base film followed by performing perforating with a laser and/or a drill, or performing perforating with a laser and/or a drill followed by stripping at least the support base film;
4) subjecting the resin composition surface to a roughing treatment; and
5) subsequently plating the roughed surface, and forming a conductor layer.
As a second embodiment of the present invention wherein a conductive paste is utilized to perform interlayer connection, there is provided a method of manufacturing a multilayered printed wiring board using an adhesive film comprising a support base film provided with a mold release layer and a thermosetting resin composition laminated on the surface of the mold release layer, said resin composition being provided with the same or smaller area as or than that of the support base film, provided with thermal fluidity and being solid at normal temperatures,
said method further comprising essentially the steps of:
1) directly covering at least the pattern processed portion on one surface or both surfaces of a pattern processed circuit substrate with the resin composition layer of said adhesive film, and performing laminating by heating and pressurizing under a vacuum condition;
2) thermally curing the resin composition followed by performing perforating with a laser and/or a drill;
3) charging the conductive paste into the resulting hole(s);
4) uncovering the resin composition layer by stripping at least the support base film followed by thermally curing the conductive paste, or thermally curing the conductive paste followed by stripping at least the support base film;
5) subjecting the resin composition surface to a roughing treatment; and
6) subsequently plating the roughed surface, and forming a conductor layer.
Finally, as a third embodiment of the present invention, there is provided a method of manufacturing a multilayered printed wiring board using an adhesive film comprising a support base film provided with a mold release layer and a thermosetting resin composition laminated on the surface of the mold release layer, said resin composition being provided with the same or smaller area as or than that of the support base film, provided with thermal fluidity and being solid at normal temperatures,
said method further comprising essentially the steps of:
1) directly covering at least the pattern processed portion on one surface or both surfaces of a pattern processed circuit substrate with the resin composition layer of said adhesive film, and performing lamination by heating and pressurizing under a vacuum condition; and
2) thermally curing the resin composition with the support base film being attached thereto whereby an insulation layer is formed.